1. Field of the Invention
The present invention relates to an information acquisition system, and more particularly to an information acquisition system for acquiring necessary map data from an external information center outside a vehicle.
2. Description of the Related Art
A technique for acquiring map data, which is to be used in navigation of a vehicle, from an external information center is currently known.
This prior art is exemplified by Japanese Patent Laid-Open Publication No. Hei. 7-262493, which discloses a system for distributing, through communication media between a vehicle and an external information center, map information commensurate with the degree of detail needed in smooth running of the vehicle. Namely, the user requests distribution of detailed map information from the information center as required, or the system automatically requests detailed map information from the information center when the vehicle comes leaves the area of the present detailed map information. Thus the system receives the new map information newly distributed from the information center.
However, if the vehicle runs into a blind area in which detailed map information is not acquirable via any communication media, then the vehicle cannot keep running smoothly without consulting with the detailed map of the blind area.
It is an object of the present invention to provide an information acquisition system for acquiring map information of a blind area, where the map information is not acquirable from an external information center, without fail, even when the vehicle runs in the blind area, thus enabling the vehicle to keep running smoothly.
According to a first aspect of the invention, the above object is accomplished by an information acquisition system for acquiring map information from an external source outside a vehicle, comprising: storage means for storing specifying data of a blind area in which the map information is not acquirable; and control means for acquiring, based on the specifying data, the map information of the blind area when the vehicle approaches the blind area. The map information includes, in addition to the map data, data concerning various kinds of facilities (e.g. gas stations and restaurants). The blind area is an area within which the vehicle cannot receive the map information from the information center even if it requests the information center to supply such information. Before entering the blind area, the vehicle can acquire the map information of the blind area to keep running smoothly even in the blind area.
Preferably, the control means acquires the map information within a predetermined range from the current position of the vehicle. This predetermined range 4s preferably composed of a plurality of distance steps for each of which the control means acquires a different level of the map information. After the vehicle has passed the blind area, the map information of the blind area is no longer necessary, so it is preferable to delete the map information of the blind area.
According to a second aspect of the invention, the above object is accomplished by an information acquisition system for acquiring map information from an external information center outside a vehicle, comprising: a memory for storing specifying data of a blind area in which the map information is not acquirable; a processor for acquiring, based on the specifying data, the map information of the blind area when the vehicle approaches the blind area; and a communication device for requesting, based on a signal from the processor, the external information center for the map information and for receiving the map information transmitted from the information center.
Preferably, the memory has a first area for storing the specifying data, a second area for storing data of a map-information-acquirable area in which the map information is acquirable from the external information center, and a third area for storing the acquired map information. The processor acquires the map information of different levels commensurate with a distance from the current position of the vehicle to the blind area. If a blind area exists in a guide route from the current position of the vehicle to a destination, the processor acquires the map information of different levels commensurate with the distance from the current position of the vehicle to the blind area.